Flower formation and fruit setting in ‘Tainong No.1’ passion fruit and its relationship with meteorological factors

Abstract:【Objective】Passion fruit is an important tropical and subtropical vine crop in south China. This study aims to explore the flower formation and fruit setting characteristics of a main passionfruit variety planted in China to identify the dominant fruiting nodes and branches. Furthermore, key meteo- rological factors that affect the flowering and fruiting were studied and the crucial effective period was determined.【Methods】The main Chinese passion fruit variety‘Tainong No.1’was selected as the material for the study. Stems of different order branches including main vines (0/x), primary lateral vines (1/ x/x), secondary lateral vines (1/x/x/x) and tertiary lateral vines (1/x/x/x/x) were observed. We tagged the buds at the beginning of flower bud formation to investigate the flower bud differentiation and degeneration, fruit setting and fruit dropping at each node of the vines. According to the investigation, the differ- entiated percentage of flower bud (DIFB), degeneration percentage of flower bud (DEFB) and fruit set percentage (FSP) at different nodes and branches were calculated. Besides, the data of temperature, light intensity and relative humidity were collected synchronously in the orchard, and the correlations between the flower formation and fruit setting characteristics of different branches in different growth seasons and meteorological factors before and after flowering were analyzed.【Results】(1) DIFB of‘Tainong No.1’was 77.2%, DEFB was 41.4%, and FSP was 36.5% on average in summer and autumn. On the whole‘, Tainong No.1’displayed high a flower differentiation rate and a high flower bud degen- eration rate, but low fruit set. There was poor flower bud differentiation at the basal nodes with high flower bud degeneration incidence at the distal nodes. The DIFB, DEFB and FSP of the 4-7th nodes ranged from 84.2% to 98.0%, 22.2% to 38.8%, and 37.3% to 43.0%, respectively. These results suggest- ed that the 4-7th nodes had a higher flower bud differentiation rate with a good FSP. Therefore, these nodes were the dominant fruiting nodes. Compared with the other branches, the secondary lateral vines showed higher ratios of flower differentiation and fruit set. Flower bud characters of the basal 1-3thnodes of the primary and the secondary lateral vines were better than those above the third node in these lateral vines. (2) The DIFB and DEFB in different growth seasons showed a similar trend. From the mid-early September to the end of October, the temperature and light intensity gradually decreased, and the DIFB and DEFB of the secondary lateral vines showed an increasing trend, with a higher FSP. The results of correlation analysis showed that temperature was the most important meteorological factor af- fecting the flower formation and fruit set. We found that the daily maximum temperature and daily aver- age temperature from 20 to 35 days before flowering were negatively correlated with the DIFB and DEFB. When the daily maximum temperature and daily average temperature at anthesis were higher than 36.19 °C and 26.24 °C, respectively, the FSP decreased with the increase in temperature. Moreover, the daily maximum temperature from 5 to 20 days after anthesis was negatively correlated with the FSP in the primary and secondary lateral vines. Further analysis showed that under the conditions of diurnal maximum temperature/minimum temperature of 34.2/20.4 °C or 36.7/23.4 °C in the flower bud formation stage, flower formation was suppressed in the secondary and tertiary lateral vines. In addition, light intensity showed a greater impact on flowering at the later stage of flower bud differentiation in the range from 4.00 to 4.79 klx, with a higher DIFB and DEFB in the secondary and tertiary lateral vines. However, under low temperatures and low light, flower bud differentiation was inhibited. Besides, light intensity influenced FSP. We found the light intensity from 5 to 15 days after anthesis had a significant negative correlation with the FSP. In addition, relative humidity also affected the flower formation and fruit setting in‘Tainong No.1’. The daily average relative humidity from 20 to 35 days before anthesis and from 5 to 15 days after anthesis were negatively correlated with the DIFB and DEFB in the secondary lateral vines and the FSP in the secondary lateral vines, respectively. The relative humidity on the day of anthesis was also negatively correlated with the FSP.【Conclusion】The characteristics of flower bud formation and fruit set varied among different nodes and different branches in‘Tainong No.1’. The 4-7th nodes were the dominant fruiting nodes, and the secondary lateral vines were the dominant fruiting vines. Temperature, light intensity and relative humidity all affect the flower bud formation and fruit set. The temperature from 20 to 35 days before anthesis was the most important meteorological factor affecting flower bud formation, and the temperatures on the day of anthesis and from 5 to 20 days after anthesis had a crucial impact on and fruit set.